1. Field of the Invention
The present invention relates to a DRAM structure and a method of making the same, and more particularly to a DRAM structure that uses a conducting strap to connect a MOS transistor with a trench capacitor. An SSBL (single-sided buried strap) is replaced by the conducting strap. In this way, resistance can be reduced and current leakage can be decreased.
2. Description of the Prior Art
Electrical products are becoming lighter, thinner, shorter, and smaller, and dynamic random access memories (DRAMs) are being scaled down to match the trends of high integration and high density. A DRAM comprising many memory cells is one of the most popular volatile memory devices utilized today. Each memory cell comprises a MOS transistor and at least a capacitor, wherein the MOS transistor and the capacitor form a series connection with each other. By using a word line and a bit line, a DRAM can be read and programmed.
FIG. 1 shows a prior art DRAM structure. The conventional DRAM structure includes a MOS transistor 200 and a trench capacitor 202, wherein the MOS transistor comprises a gate conductor 204, a oxide layer 206, a source doping region 208, a drain doping region 210, and the trench capacitor 202 comprises a conductive layer 210, a bottom electrode 212, a dielectric layer 214, a cap layer 216, and a single-sided buried strap (SSBS) 218. In addition, bias can be formed between the source doping region 208 and the drain doping region 210 by using the word line 220 and bit line 222. The current or electronic charge will flow from the source doping region 208 into the trench capacitor 202 by passing the drain doping region 210 and the SSBS 218, and will then be stored in the trench capacitor 202.
The size of a modern SSBS 218 is decreased because the size of modern DRAMs has also decreased. The resistance, however, has increased due to the shrinking size of the SSBS.
Furthermore, in the conventional DRAM structure, a high electronic field will occur around the junction of the SSBS 21 8, thereby decreasing the operating effect, and causing current leakage and control problems.